This invention relates to fluid distributors, and more particularly to distributors that provide uniform distribution of either a liquid or a gas throughout a bed of granular media.
Uniform distribution of fluid in beds of granular media is important in many fluid treating systems. For example, in filters where a liquid being treated flows down through a bed of filter media, such as sand, the bed is usually supported by a filter bottom that collects the filtered liquid and also distributes a backwashing liquid that is forced up through the bed when cleaning is necessary. Uniformity of distribution of this backwash liquid is extremely important. Nonuniform distribution can leave parts of the bed contaminated after backwashing and can disrupt the bed, which reduces the life of the filter.
In some filters, a gas such as air is forced through the bed prior to conventional liquid backwashing. The air bubbles up through the filter and provides a very thorough agitation of the media, dislodging accumulated dirt and/or gelatinous floc which then can be removed easily by liquid backwashing. This type of agitation is particularly attractive for cleaning tertiary filters, in which heavy, sticky deposits are formed in the media.
With air backwashing, uniform distribution of both air and water is important. In addition, in air backwashing it is desirable to minimize expansion of the air as it passes from the filter bottom into the bed. If the air expands significantly at this point, it can disrupt the gravel support layers frequently used beneath beds of sand filter media. As a result, many filters that utilize air cleaning either deposit the sand directly on top of the filter bottom or place the air distribution system above the gravel support layer. If the sand is placed directly on the filter bottom, the passages or orifices leading from the bottom into the bed must be extremely small to keep sand out of the filter bottom. This situation frequently leads to plugging of the underdrain. On the other hand, placing an air distribution system above the gravel support layer requires two separate systems and increases the cost of the installation.
One prior art system that provides extremely uniform distribution of a liquid backwashing medium is disclosed in U.S. Pat. No. 3,110,667 to Mark L. Stuppy. This system utilizes filter bottom blocks having upper and lower lateral conduits extending from block to block across the filter. The lower or primary lateral conduits are connected to a flume, through which the backwash liquid is supplied. Ports connect the lower laterals to the upper or secondary laterals, and additional ports connect the secondary laterals to the filter bed. Thus, the backwashing liquid passes from the flume along the lower or primary laterals, into the secondary laterals, and from there into the filter bed.
Since the upper or secondary laterals extend from block to block along the rows, the backwashing liquid can flow along them to compensate for any inequalities in the flow from the primary to the secondary laterals. If the primaries are supplied equal amounts of water, this dual lateral system provides extremely uniform distribution of the backwash liquid across the entire filter bottom. However, if there are variations in the amount of water supplied to individual primaries, as might occur due to roughness, construction tolerances or the like or if a primary was partially blocked, the flow from the secondaries to the bed will vary in a similar manner. Also, the system has no provision for air backwashing, which would be desirable in many installations.